> I have a hard time to comprehend how this can be considered a reasonable security measure. OK, let's walk it through. Task: block access to "attacker.com" a

> I have a hard time to comprehend how this can be considered a reasonable security measure. OK, let's walk it through. Task: block access to "attacker.com" and all it's subdomains. Reason: Maybe it's a malware command and control, maybe it's being used for DNS tunneling, whatever. Blocking a domain that's being used for malicious behavior is a reasonable thing for an enterprise to want to accomplish. Option 1: Block by IP at the firewall. Problems: Attackers can simply point the domain to another IP, so you're constantly playing whack-a-mole and constantly behind the attacker. Also, if it's a DNS tunnel the DNS answer is what's interesting, not the traffic to the actual IP. Result: Fail, doesn't solve the problem. Option 2: Block by DNS Name at the firewall. Problems: Requires the firewall to understand the protocols involved, which they have shown themselves to be inconsistent at, at the best of times. Also, doing regex on every DNS query packet(in order to find all subdomains) doesn't scale. Result: Fail, doesn't scale. Option 3: Block with local agent. Problems: Tablets, phones, appliances, printers can't run a local agent. Result: Fail. Not complete coverage Option 4: Block outbound DNS except for approved resolvers, give those resolvers an RPZ feed of malicious domains. Problem: Clients have to be configured to use those resolvers, but otherwise none. Result: Pass. It's standards compliant, and DNSSec isn't an issue since the resolver never asks for the attackers DNS answer, so they never get the chance to offer DNSSec. That's why option 4 (or some variant of it) is popular in enterprises. It accomplishes the task in a standards-compliant way, and covers the entire enterprise in a way that scales well. DOH blows this up. So, the question becomes: in a world with DOH, how is an enterprise supposed to completely and scalably block access to "attacker.com" and all its subdomains? So far, the answer has been "you don't." I think that is a really shitty answer to someone who's trying to accomplish something reasonable.